The present description relates generally to optical sensors, and more particularly to interrogation methods of Fabry-Perot based optical pressure sensors for measuring static and dynamic pressures over a wide bandwidth range at high temperatures.
Pressure sensors are used in a wide range of industrial and consumer applications. Pressures of many different magnitudes may be measured using various types of pressure sensors, such as Bourdon-tube type pressure sensors, diaphragm-based pressure sensors and piezoresistive pressure sensors on silicon or silicon on insulator (SOI). Several variations of the diaphragm-based pressure sensor have been utilized to measure different ranges of pressure, such as by utilizing cantilever-based pressure sensors, optically read pressure sensors and the like.
Fiber optic sensor utilizing a Fabry-Perot cavity have been demonstrated to be attractive for the measurement of temperature, strain, pressure and displacement, due to their high sensitivity. Some advantages of fiber optic sensors over conventional electrical sensors include immunity to electromagnetic interference (EMI), resistance to harsh environments, small form factor and potential for multiplexing.
In some instances the Fabry-Perot cavity is formed by a diaphragm, which deflects under pressure. The cavity is illuminated with a visible or infrared light source and a varying amount of that light is both reflected by and transmitted through diaphragm. When the light reflects back toward the source, there is constructive and/or destructive inteference of the light with the incident beam characteristic of the length of the Fabry-Perot cavity. When the diaphragm is deflected as a result of quantity to be measured such as applied pressure, force, stress or strain (herein referred to as the measurand), the interference behavior changes due to the change in the length of the Fabry-Perot cavity.
The main challenges in converting diaphragm deflection into a usable linear output include maintaining adequate optical signal levels to overcome noise in the receiver while attempting to make the system immune to any fluctuations other than those of the sensor itself. Typical fluctuations might include intensity fluctuations of the interrogating optical source, mechanical fluctuations within the optical path, and temperature-induced fluctuations in the system.